Gardening Articles: Landscaping :: Trees, Shrubs, & Vines

Shopper's Guide to Bark Mulch

by Charlie Nardozzi

The advantages of using organic mulch to blanket soil around trees, shrubs, and perennial plants are many: Mulch moderates soil temperature and makes a more favorable environment for roots. It reduces evaporation of moisture, helping to conserve water. It reduces splashing from rain or irrigation water, reduces the spread of disease, and blocks the germination of many weed seeds. Beyond all that, a mulch dresses up your garden, giving it a more finished look.

This article explores the kinds of bark mulches you can buy and their advantages and disadvantages. Several bark and wood mulches are available--bark nuggets, mini-nuggets, hardwood mulch, and shredded mulch. Some come in bags, some in bulk. A chief advantage of these mulches compared with other organic mulches is that they remain attractive and functional for a couple of years. That's why gardeners mulching around trees, shrubs, and other long-lived plants are wise to choose a long-lasting bark mulch.

The Difference Between Wood and Bark Mulch

According to the National Bark & Soil Producers Association, any mulch with "bark" in the name must be at least 85 percent bark of that named tree. A "mulch" material, on the other hand, need be only 70 percent of the named material, and it may be either bark or wood. In both cases, the remaining 15 or 30 percent can be just about anything, but it is usually wood.

The primary difference is how long the mulch will last before breaking down. "Wood breaks down quicker and is more susceptible to insect damage and discoloring than bark," explains Bob LaGasse, executive director of the NBSPA.

Nitrogen Deficiency

Decomposing wood requires nitrogen. If you add a quantity of, say, fresh sawdust to your garden soil, chances are your plants will suffer from a lack of nitrogen. In this case, the soil isn't necessarily deficient, but the breakdown of the sawdust "induces" nitrogen deficiency in your plants. Wood and bark mulches can also induce nitrogen deficiency, but it isn't likely because they decompose at such a slow rate. It's also unlikely because they are on top of the soil, not incorporated at root depth. But if this concerns you, or if your plants show the signs of nitrogen deficiency, add a 2-1-1 ratio fertilizer, such as 20-10-10, before mulching (2 to 5 pounds per 500 square feet).

Agricultural By-products

Exotic mulches are usually agricultural by-products and are often (or only) available in bulk. One big advantage is their very low cost. Most are available only seasonally and only in certain areas of the country. Some examples of these include cottonseed, buckwheat, corncobs, grape pomace, pine straw, and pecan, walnut, and rice hulls.

Although many exotic mulches are attractive and less expensive to use, they can be hard to find and may attract insects, such as ants. Plus, they tend to break down quickly. Ask your local Extension agent or garden center about the availability of this kind of mulch in your area.